How do you get a low poly exterior from a high poly model?
i had models like that too before i was able to create my own projects... here's how i made most of them usable...
to connect the vertices, simply select the coplete object in edit mode. then hit OBJECT/VERTICES/REMOVE DOUBLE.
to reduce the size (# of vertices), switch to OBJECT MODE, go to MODIFIERS and select DECIMATE. there choose for UNSUBDIVIDE if the model is created mainly in quads. change the ITERATIONS value until the model still looks acceptable and hit APPLY.
if the model is created in tri's, choose for COLLAPSE and change the RATIO value (in OBJECT MODE) until the model still looks acceptable and hit APPLY.
hope this helps